1. Field of the Invention
The present invention relates to systems for spraying a liquid emulsion and a solvent for the emulsion, and more particularly to systems which spray liquid asphalt emulsion onto roadway surfaces for roadway distress and pothole repairs and which are cleansed by a solvent for the emulsion.
2. History of the Prior Art
According to the Asphalt Institute, pavement repair requires certain procedures and specific materials for each case of roadway distress or damage. A pothole is an example of localized roadway distress which requires "Full depth asphalt patching." The method for repairing this type of condition requires the following equipment and procedures to be used:
a. Using a pavement hammer or saw, an area is excavated and sides are cut in rectangular with vertical faces. PA1 b. Subgrade is dried and compacted. PA1 c. A tack coat of liquid asphalt emulsion (LAE) is applied by a sprayer to the sides of the rectangular cut. PA1 d. The hole is backfilled with hot plant mixed asphalt cement. PA1 e. The new material is rolled flat to complete the repair. A vibratory compactor is used on small repairs.
A common method for roadway maintenance crews to transport the equipment needed for the above procedures is to use a dump truck loaded with hot asphalt cement and pulling a sprayer for LAE and a smaller truck pulling an air compressor to run an air hammer. If the area to be patched is large, a third truck is needed to pull a roller. Some pavement maintenance crews are equipped with a special dump truck with either an air compressor or hydraulic units to operate the air or hydraulic pavement hammer and LAE sprayer mounted onto the truck body. The truck is also equipped with a trailer hitch to pull a roller when necessary. The latter method is especially suited to repairing small damaged areas such as potholes, where small amounts of materials are used in a variety of localities.
National attention has been given to the repair of minor roadway damage. Potholes have become so numerous that large areas of roadways are further endangered because the water protection to the subgrade is eliminated, not to mention the hazards to safety and damage to car and truck steering systems which result if the pothole is not repaired.
Considering the procedures required to repair pothole areas and often the bad weather conditions which affect not only the heated materials but the personnel required to work, improvement in productivity will come only with an improvement in the equipment and work methods used. For this reason, the use of hydraulic hammers and hydraulic LAE sprayers has become more popular. The rising cost of air compressors compared to the cost of a hydraulic pump and the recent technical developments in hydraulic hammers have prompted this change. It appears that maximum production of pothole repairs will occur with the use of a single truck system and a small three man crew. Because hydraulic power uses less space and costs less than air systems sized large enough to run an air hammer, there will most likely be an increase in the use of this type of system. Much work has been done to increase the acceptability of the hydraulic hammer which is required if the air hammer and compressor is not provided. However, a need for the improvement of the LAE sprayer exists in any event.
Observation has shown that when potholes are repaired in bad weather, the use of LAE is often eliminated from the procedure, contrary to proper practice. This is largely due to the fact that LAE is required to be at a warm temperature (100.degree.-140.degree. F.) and also has a very unstable nature when heated frequently, as is the case when the material is stored in large quantities, and used in small quantities. LAE consists of a paving grade asphalt which has been heated to 250.degree.-325.degree. F. and mixed with water blending with surfactants, stabilizers and emulsifiers. If the water content of the resulting emulsion is reduced by evaporation caused by reheating, the emulsion develops "shot" or congealed solids of asphalt which are usually dispersed in the emulsion. For this reason, LAE is considered unstable and care to prevent deemulsification must be taken. Frequent heating can easily evaporate the water solvent and the small pressure needed to spray the material (about 50 psi) can also increase the tendency to promote solids in the sprayer distributor, especially if the water solvent quantity has been reduced. Minimum temperature for LAE is 70.degree. F. for sprayer application, while 100.degree. F. is optimum. Some LAE materials require a higher sprayer liquid temperature.
Experience has shown that the best way to keep an LAE sprayer operating and dependable is to flush the system with solvent after each use of the sprayer. The solvent employed is usually No. 2 fuel oil or diesel fuel. When plugging of solids occurs, further pumping of LAE to remove the plugs can result in even more plugging by causing the compaction of the LAE. Even when precautions such as insulating the LAE reservoir to prevent frequent reheating and the use of a filter upstream of the LAE pump with frequent cleaning are taken, LAE solids are encountered in the spraying of LAE during times of high production unless frequent flushing of LAE is accomplished.
In one conventional LAE sprayer, by way of example, separate sources of LAE and solvent are coupled to a common pump which pumps one or the other through a spray wand. Two different ball valves must be closed each time it is desired to switch from spraying LAE to solvent to cleanse the sprayer. Consequently use of solvent is infrequent, and buildup of clogging LAE solids is common. At that, the common pump which is designed to optimize pumping of LAE is ill-suited for use with solvent. The pump is incapable of withstanding the higher pressure needed for the solvent to be effective, and attempts to raise the solvent pressures usually result in the pump seal being broken.
Accordingly, it would be desirable to provide an LAE sprayer which is easily switched from spraying LAE to solvent for cleansing or other application of the solvent. The solvent should ideally be available at high pressure without damage to pumps and other equipment in the system and without danger of backflowing or other intermixing with LAE.